1. Field of the Invention
The present invention relates to an electromagnetic spool valve system including a linear solenoid section and a spool section.
2. Description of the Related Art
A conventional electromagnetic spool valve is usually constituted by a spool valve having an approximately cylindrical outer shape and a solenoid section functioning as an electromagnetic actuator to actuate the spool valve.
As for such an electromagnetic spool valve, the present applicant has provided a linear solenoid valve that realizes significant enhancement of magnetic attractive force to a movable core, as disclosed in JP 2005-286236 A, for example.
In such a linear solenoid valve disclosed in JP 2005-286236 A, there are provided an inlet port and an outlet port on an outer circumference of a cylindrical valve body, and also a single spool within the valve body, which moves along the axial direction so as to switch a state of communication and discommunication between the inlet and outlet ports.
The linear solenoid valve disclosed in JP 2005-286236 A, in response to control signals from the controller, controls the solenoid section (coil) to be in off state (i.e. current supplied state) or in on-state (i.e. non-current supplied state) using duty ratio control, so as to provide a two-state (communication and discommunication) switching control between the inlet and outlet ports, which allows the two-state switching control on hydraulic pressure.
In this case, the linear solenoid valve disclosed in JP 2005-286236 A provides the above-mentioned two-state switching control for the hydraulic pressure led out of the outlet port by sliding the single spool. However, multi-state switching control for hydraulic pressure in a more accurate way has been desired.
In addition, it has been desired that, even in the multi-state switching control for hydraulic pressure carried out by using multiple spools, spool-operating delay is reduced to as small as possible at the time of state-switching control for the hydraulic pressure, so as to enhance the valve-operational responsiveness.